The problem of rerouting/protecting traffic in communication networks is one of the main topics, which is being permanently discussed and developed to improve efficacy of networks operation.
Ring networks have largely evolved in local area computer networks (LANs). Their main benefits are: ability to add/drop local data to/from the ring at any local station while passively forwarding traffic which doesn't belong to a particular local station; efficient use of cables, for example in comparison with mesh networks; fault recovery of traffic, since two-way links between stations can be used for redirecting the traffic in case of a cable break. SDH/SONET networks have adopted these advantages to implement multi point-to-point connections within the ring. Yet, SONET/SDH ring protection is inefficient compared to packet-based protection and often creates bandwidth bottlenecks at a metro level.
Protection of traffic in ring networks is ensured by the intrinsic features of ring networks. According to the most schematic principle concept, a ring-like network is composed of two “concentric” sub-rings (a 1st ring and a 2nd ring) formed by network nodes interconnected via communication links and respectively enabling traffic in the ring-like network to flow in two opposite directions. In case of failure of a particular link belonging to a 1st ring, protection of the traffic which was transmitted via the 1st ring is performed by redirecting it, at two nodes surrounding the faulty link, so as to utilize the 2nd ring and thus reach the required nodes “from the other side”. The 2nd ring (as well as the 1st ring) usually reserves bandwidth for such cases and provides a so-called protection path instead of a main path section failed in the 1st ring.
As MPLS technology becomes more and more practically demanded, it is often deployed over existing ring networks and is therefore to be protected in such networks. Fast reroute (FRR) has gained substantial traction in the vendor community and interest from service providers. It offers high speed recovery following network failures, and thereby can shorten disturbance to traffic and improve the service reliability. Fast reroute in packet-based networks brings service providers closer to the point where they can provide reliability comparable to that of TDM services like SDH/SONET or voice.
The prior art comprises some solutions for protecting MPLS traffic in various networks, and also in ring networks.
US 20030108029A1 describes a method and a system for providing failure protection in a ring network that utilizes label switching. A working label switched path (LSP, also called tunnel) between neighbor label switched routers (LSRs) in a ring network that utilizes label switching is protected by an LSP that connects the neighbor LSRs of the working LSP in an opposite direction to the working LSP. If the working LSP fails, then packets are switched to the protection LSP. Switched packets traverse the protection LSP until they reach the neighbor LSR that they would have reached had the packets traversed the working LSP. Time-to-live (TTL) values of packets that traverse the protection LSP are adjusted to account for the number of hops on the protection LSP so that the TTL values of the packets are the same after traversing the protection LSP as they would have been had they traversed the working LSP. After traversing the protection LSP packets can be switched back to the working LSP or switched to a next hop LSP. However, in case of a failure in the ring, the solution makes the traffic to pass so-called excessive portions over the main and the protection paths (as the ring networks dictate), to reach the required termination (egress) node. As a result, the solution suffers from a traffic delay, is critical to multiple faults in the ring and is inefficient from the point of bandwidth reserved for ensuring protection in the excessive portions of the ring.
US20020093954A1 describes a technique for failure protection in communication networks. A communications packet network comprises a plurality of nodes interconnected by communication links and in which tunnels are defined for the transport of high quality of service MPLS traffic. The network has a set of primary traffic paths for carrying traffic and a set of pre-positioned recovery (protection) traffic paths for carrying traffic in the event of a fault affecting one or more of the primary paths. The network incorporates a fault recovery mechanism. In the event of a fault, traffic is switched temporarily to a recovery path. The network then determines a new set of primary and recovery paths taking account of the fault. The traffic is then switched to the new primary paths. The new recovery paths provide protection paths in the event of a further fault. The network nodes at the two ends of a recovery path exchange information over that path so that packets returning to the main path present their original labels that are recognizable for further routing of those packets.
US20020060985A1 discloses a method for high speed rerouting in a multi protocol label switching (MPLS) network which can minimize a packet loss and enable a fast rerouting of traffic so as to protect and recover a multi point to point LSP occupying most LSPs in the MPLS network. The method for high speed rerouting in a multi protocol label switching (MPLS) network comprises the steps of controlling a traffic stream to flow in a reverse direction in a point where a node or link failure occurs by using a backup Label Switched Path (LSP) comprising an Explicitly Routed (ER) LSP having a reverse tree of a protected multi point to point LSP and an ingress LSR through an egress LSR. The method suffers from the drawbacks mentioned before, since it enforces the backup path to return the traffic into the ingress point of the ring where the LSP has started.